Although electronic devices such as semiconductor integrated circuits are often constructed on silicon single crystal substrates, single crystal substrates made of gallium nitride GaN having better electric characteristics are expected to be used for power devices etc. requiring a function of controlling comparatively large electric power, instead of the silicon single crystal substrates. Since a power device using such a single crystal substrate made of gallium nitride GaN can deal with a large amount of electric power, generates small amount of heat, and can be miniaturized, the power device is preferably used as a control element controlling the number of rotations or torque of a motor or an electric generator in a hybrid vehicle, a fuel-cell vehicle, etc. The single crystal substrates made of gallium nitride GaN are excellent in high frequency characteristics and are expected to be developed into wireless communication stations, relay stations, mobile stations, etc.
In a typically employed manufacturing method employed for manufacturing of VLSI, a multiplicity of chips are formed on a semiconductor wafer, which is cut into respective chip sizes in a final process. Since a degree of integration is recently dramatically increased in association with improvements in VLSI manufacturing technology and wirings are increasingly multilayered, planarization of an entire semiconductor wafer (global planarization) is required in a process of forming each layer. One of the techniques of achieving such planarization of an entire semiconductor wafer is a polishing method referred to as a CMP (chemical mechanical polishing) method. In the CMP method, while a nonwoven fabric or a polishing pad such as a foam pad affixed to a surface plate is pressed against a wafer and forcibly rotated, a slurry (a dense suspension with fine powder dispersed in liquid such as an aqueous alkali solution) containing fine polishing particles (loose abrasive grains) is allowed to flow thereto for polishing. This CMP method achieves comparatively accurate polishing processing because of a synergetic effect between chemical polishing with a liquid component and mechanical polishing with polishing abrasive grains.
However, in such a conventional CMP method, a considerable time is spent for the polishing processing. If a loose abrasive grain polishing processing using diamond abrasive grains as polishing particles is performed, surface roughness becomes as large as Ra=10 nm, for example, although a certain level of processing efficiency is provided. In contrast, if a loose abrasive grain polishing processing is performed by using silica abrasive grains, the surface roughness becomes smaller; however, the processing efficiency deteriorates and scratches of unknown cause inconveniently tend to occur.
In this regard, a polishing processing method for polishing a SiC single crystal substrate is proposed. For example, this corresponds to a polishing processing method described in Patent Document 1.